Sulfenamides



Patented Jan. 28, 1947 SULFENAMIDES George E. 1?. Smith, Jr., Akron, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Original application October 30,

1941, Serial No. 417,163. Divided and this application October 12, 1944, Serial No. 558,461

5 Claims. 1

This invention relates to the vulcanization of rubber, and relates especially to a new class of chemical compounds which are valuable accelerators for the vulcanization of rubber or rubber-like substances. This specification is a division of my copending application Serial No. 417,163, filed October 30, 1941, now Patent No.2,367,827.

It is a primary object of the present invention to provide a new class of accelerators for the vulcanization of natural or synthetic rubber.

Another object is to provide a class of improved rubber vulcanization accelerators of the delayed action, non-scorching type.

Another object is to provide a class of improved rubber vulcanization accelerators, which are solids, easily incorporated in rubber, stable in storage, and commercially practical.

The above and further objects will be manifest in the description of the invention which follows.

It has been found that members of a new class of chemical compounds are very effective in accelerating the vulcanization of natural or synthetic rubber. The new compounds may be conveniently prepared by oxidizing a mixture of an aromatic Z-mercaptothiazole and a dialkylor trialkyl-carbinamine. The preparative oxidation reaction may be effected by treating a mixture of the mercaptothiazole and an excess of the amine in an alkaline aqueous medium with one of the following oxidizing agents: chlorine, bromine, iodine, hypochlorous acid,hypobromous acid, hypoiodous acid, and alkali metal and alkaline earth metal salts of said acids. The oxidation reaction is believed to comprise the direct action of a hypohalous acid, or an alkali metal or an alkaline earth metal salt thereof, on a mixture of the mercaptothiazole and one equivalent of the amine. The desired substances produced by this oxidation reaction are organic compounds containing nitrogen and sulfur.

This new class of accelerators is believed to possess the following type formula:

wherein Ar is an orthoarylene radical, R. and are alkyl radicals, and R" is hydrogen or an alkyl radical. Thus, the new compounds are b lieved to be derivatives of sulfenamide (HSNHz). Examples of orthoarylene radicals include benzo, 4-phenylbenzo, 6-phenylbenzo, naphtho, and homologs or the various ring substitution products of these radicals; as typical ring substituents there may be mentioned nitro, halogen, hydroxy and alkoxy groups. Examples of alkyl radicals include methyl, ethy1,'propyl, butyl, amyl, hexyl, heptyl, octyl and similar radicals.

The following specific examples are given in further illustration of the invention.

Example 1 N lllOHs The above sulfenamide was tested as an accelerator by comparing it with the standard accelerators, mercaptobenzothiazole and dibenzothiazyl disulfide, the latter being a delayed action accelerator, in the iollowing rubber formula:

Ingredients 32E2 3? Rubber (smoked sheets) 100. on Sulfur 3.00 Zinc oxide. 5.00 Stearic acid 1. 10 Acceleraton 0.

Samples of the three rubber compositions, so

formulated, were heated for 30 minutes at 240 F. to determine whether or not they possessed any tendency to pre-vulcanize or set-up during processing steps prior to the usual vulcanizing step, and the following physical testing data were obtained:

Modulus of ellgstlicity in tTenstille s. in. at s reng in Accelerator elongation lbs/in. at

of 600 perbreak cent Mercaptobenzothiazole 375 2,175. Dibenzothiazyl disulfide N cure..- No cure. N-isopropyl-2-benzothiazyl sulfenamida do Do.

Other samples of the aforesaid rubber compo- 4 sec. hexylamine (methyl-isobutyl-carbinamine). The following stable, white solids were obtained in good yields:

2-benzotl1iazyl sulfenamide Melting point C. N-sec. butyl- 59-61 N-sec. amyl- (or N-methyl-n-propyl-carbi.n-) l 58-60 N-sec. hexyl- (or N-methyl-isobutyl-carbin-) 52-54 Modulus of elasticity Tensile trength in Accelerator in lbs/in. at 600 percent elongation at break Cure in minutes 60 30 00 Mercaptobenzothiazole 400 750 1 2,250 2,800. Dibenzothiazyl disulfide N o cure... N o cure. N o cure No cure N-sec. butyl-2-benzothiazyl sulienamide d do o Do. Nsec. amyl-2-bcnzotl1iazyl sulfenamide H dom Do. Nsec. hexyl-2-benzothiazyl sulfenamlde v i do Do.

sitions were Heated for 20 minutes at 280 F. to

determine the relative accelerating properties of Other samples of the same rubber compositions were heated at 280 F. for 20 and 40 minutes, and the following data were obtained:

Modulus of elasticity Tensile Strength in Accelerator in lbs/in. at 600 per- I cent elongation lbs/in. at break Cure in minutes 20 40 20 40 Mercaptobenzothiazole v 650 650 2, 550 2, 700 Dibenzothiazyl disulfide V 1 l l 450 700 2, 150 2, 725 N-sec. butyl-2-benzo-thiazy1 sulfenam 1de. 950 2, 900 2, 825 3, 625 N-sec. amyl-2-benzo-thiazyl sulfenamldem l, 550 2, 650 3, 350 3, 900 N-sec. hexyl-2-benzo-thiazyl .1 700 2, 800 2, 675 3, 000

the respective accelerators, and the following data were obtained:

Modulus of ellgstlicity tTenszllle s. in. a s reng 1n Accelerator elongation lbs/in, at

of 600 perbreak cent Mercaptobenzothiazole 650 2, 550 Dibeuzothiazyl disulfide 525 2, 450 N-isopropyl-2-benzothiazyl sulfenamide 2, 225 K 4, 250

Example 2 Three further sulfenamides were prepared by the procedure of Example 1, the 12 molecular parts of isopropylamine of that example being replaced successively by 9 molecular parts of sec. butylamine (methyl-ethyl-carbinamine), 5 molecular parts of sec. amylamine (methyl-npropyl-carbinamine), and 5 molecular parts of The two sets of data appearing immediately hereinabove further demonstrate that sulfenamide derivatives obtainable from orthoarylenemercaptothiazoles and dialkyl carbinamines are excellent delayed action accelerators for th vulcanization of rubber.

Example 3 Ten grams of mercaptobenzothiazole were dissolved in a water solution of 5 grams of sodium hydroxide, and the resulting solution was mixed with 21 grams of tert. amylamine (dimethylethyl carbinamine). The mixture was stirred, and a potassium iodide solution containing 15.2 grams of free iodine was gradually added thereto during the course of 3 hours. The reaction mixture was extracted with ether, the ether was then evaporated, and the resulting residue was recrystallized from petroleum ether. The recrystallized product was a white crystalline solid melting at -82 C., and is believed to be N-tert. amyl-2- benzothiazyl sulfenainide, of the formula.

The new product was tested as an accelerator in the formula given in Example 1, the same control accelerators being used, and the curing time being and 40 minutes at 280 F. The follow ing physical testing data were obtained:

The above data show that the sulfenamide from a trialkyl carbinamine i a ver effective accel' erator at normal vulcanizing temperatures. Other tests have indicated that the new product is a practical delayed action accelerator, causing no vulcanization of a rubber compound under usual u processing conditions at which a corresponding compound containing the accelerator, mercaptobenzothiazole, becomes partially vulcanized or set-up.

The preferred class of sulfenamide derivatives may be prepared by other methods than those mentioned hereinabove, as will be apparent to one skilled in the art. Forexample, a mixture of an aromatic Z-mercaptothiazole and a dialkylor trialkyl-carbinamine may be oxidized by hydro gen peroxide or other conventional oxidizing agent. The invention is not limited to derivatives prepared in accordance with any particular method, but includes the preferred class of accelerators, however they may have been manufactured.

The new accelerators are equally efiective in rubber tread compounds, latex compounds or other conventional vulcanizable compounds of rubber or synthetic rubber. The various vulcanizable synthetic rubbers are herein considered equivalent to rubber, examples being the buna types (polymers essentially derived from butadiene), such as buna N (copolymer of butadiene and acrylonitrile) and buna S (copolymer of butadiene and styrene). Although sulfur has hereinabove been mentioned as the vulcanizing agent preferred in practicing the invention, other conventional vulcanizing agents susceptible to acceleration are contemplated.

The preferred compounds are seen to be very rapid accelerators at conventional vulcanizing temperatures, imparting unusually high modulus and tensile characteristics to the vulcanized rubber, but they are of thedelayed action type, in that vulcanizable compositions including them do not set-up or pre-vulcanize under conventional rubber processing conditions. The vulcanized products have been found to be highly efficient,

having low hysteresis characteristics, and to be unusually resistant to deterioration on flexing or aging.

A further common characteristic of the new class of accelerators, which has an important bearing on their practicality, is their chemical stability in storage. Various members of the preferred class have been stored and have been found to be substantially or completel unchanged after several months. In contrast to this stability, it has been observed that, under similar storage conditions, certain members of the general class of compounds, N-alkyl-Z-arylenethiazyl sulfenamides, to which the preferred class belongs, are substantially decomposed after only a few weeks or months. Such unstable compounds include N-n-amyl-2-benzothiazyl sulfenamide and N-ethyl-Z-benzothiazyl sulfenamide, and are not members of the preferred class of accelerators herein.

Conventional accelerator activators may be employed to an advantage with the new class of accelerators when extremely rapid vulcanization is desired, especially at lower temperatures. Also, the new accelerators may be used in combination with other accelerators, such as guanidine (e. g., diphenyl guanidine) or a conventional mercaptothiazole derivative (e. g., mercapto-benzothiazole or dibenzothiazyl disulfide), in order to produce rubber compositions having especially rapid or specific vulcanizing properties.

Although the invention has been described in detail in accordance with the requirements of the patent statutes, it is not limited to the specific examples given herein. The invention includes all features of patentable novelty residing in the foregoing disclosure.

What is claimed is:

1. N-isopropyl-2-benzothiazyl sulfenamide.

2. N-sec. buty1-2-benzothiazy1 sulfenamide.

3. An N-sec. amyl-Z-benzothiazyl sulfenamide, having the formula 4. A substance having the formula sulfenamide.

GEORGE E. P. SMITH, J R.- 

